NASA maps reveal dinosaur-killer

From Canada to Central America, many grandeurs of North America’s diverse topography are visible in a recently released high-resolution map from NASA’s Shuttle Radar Topography Mission. However, a relatively obscure feature, all but hidden in the flat limestone plateau of Mexico’s Yucatan Peninsula, emerged as the initial showstopper from the mission’s first released continental dataset. The existence of the impact crater known as Chicxulub (Chik-sah-loob) first was proposed in 1980. In the 1990s, satellite data and ground studies allowed it to gain prominence among many scientists as the long sought-after “smoking gun” responsible for the demise of the dinosaurs and more than 70 percent of Earth’s living species 65 million years ago. Now, the Shuttle Radar Topography Mission has provided the most telling visible evidence to date of a 112-mile-wide, 3,000-foot-deep impact crater, the result of a collision with a giant comet or asteroid.

The Chicxulub data show a subtle, yet unmistakable, topographic indication of the impact crater’s outer boundary: a semicircular trough 10 to 15 feet deep and three miles wide. Scientists believe the impact, centered off Yucatan’s coast in the Caribbean, disturbed the subsurface rocks, making them unstable. The rocks were subsequently buried by limestone sediments, which erode easily. The crater rim’s instability caused the limestone to fracture along the rim, forming the trough. In addition, the collapse of numerous limestone caverns above the crater rim resulted in an arcing chain of sinkholes, called cenotes, that are visible as small, circular depressions.

Exactly how the Chicxulub impact caused Earth’s mass extinctions isn’t known. Some scientists think it threw massive quantities of dust into the atmosphere, blocking the sun and stopping plants from growing. Others believe sulfur released by the impact led to global sulfuric acid clouds that blocked the sun and fell as acid rain. Another possibility is global wildfires triggered by atmospheric reentry of red-hot debris. The Shuttle Radar Topography Mission, flown Feb. 11-22, 2000, made 3-D measurements of the more than 80 percent of Earth’s landmass located between 60 degrees north and 56 degrees south of the equator, areas home to nearly 95 percent of the world’s population.